Recognizing the rubbing of a user's input action in AUI (Acoustic User Interface) is not easy. In particular, in the case of the sound wave pad with a relatively smooth surface, it is not difficult to generate a tapping signal of a user and recognize it, but it is difficult to generate a signal rubbing the sound wave pad by a user and recognize it.
In order to recognize the rubbing action of a user, a common sound wave pad forms the embossing (slight relief or intaglio pattern) on its surface, and through this, amplifies the sound waves generated by the rubbing. However, even if the sound waves are generated as the above described, it is even more difficult to recognize the direction of rubbing on the sound wave pad consisting of the same medium.
Generally, in order to recognize the rubbing direction on the sound wave pad, the embossing generating the sound quality which is different from each other depending on the direction is also formed. However, this embossing surface treatment must use a complicated analysis algorithm for separately recognizing the rubbing direction through the generated sound quality as well as the cost is increased due to the treatment.